Self-organized criticality emerges in dynamical complex systems driven out of equilibrium, and characterizes a wide range of classical phenomena in physics, geology and biology. However, for decades now, it remains a fundamental open question whether this broad property also finds a place in the quantum regime. In the talk, we shall present the first example of quantum self-organized criticality, emerging from quantum fluctuations and controlled by quantum coherence. We shall introduce a many-body quantum-coherently driven nanophotonic system where heavy photons interact in the presence of active nonlinearities. In this system, we shall show how quantum self-organized criticality emerges in an inherently new type of light localization, arising from two first-order phase transitions and being robust to dissipation, fluctuations and many-body interactions. The observed localization exhibits emergence of scale-invariant power laws and absence of finely-tuned control parameters. In analogy with the regime of quantum criticality at Tc = 0 in equilibrium static systems, we find that for our nonequilibrium dynamical system there exists a range of parameters for which the effective critical ‘temperature’ drops to zero, at which point we enter a fundamentally new regime of phase transitions – the quantum self-organized critical regime. We shall also approach the problem from a thermodynamic and information-theory perspective, deriving the multidimensional-state-vector Fokker-Planck (FP) equation for the distribution function of our problem, applying the maximum information entropy principle to make unbiased estimates on the probability distribution of microscopic states of our active nanosystem, and finally determining and analyzing the information gain and efficiency of the complex nanosystem close to its critical points.

Acoustic zero index metamaterials such as density-near-zero metamaterials have received increasing attention due to their potential applications on beam forming, cloaking, wave tunneling, and imaging. High transmission resulted by impedance matching of such zero index metamaterials and surrounding media requires the effective density and inverse bulk modulus to be simultaneously zero. Metamaterials possessing this property are called double zero index metamaterials. The design of double zero index metamaterials needs scatterers with sound speed lower than the background medium, which is extremely challenging for air acoustics because the air sound speed is among the lowest. This challenge can be solved for high order waveguide mode by designing structures with larger thickness. An experimental scan of the pressure field inside our design metamaterial excited by a point source reveals the existence of a Dirac cone at the Brillouin zone center. The measured envelope of the propagating wave inside the metamaterial shows double negative, double positive, and double zero properties below, above, and at the Dirac point,respectively. This result is confirmed by the measured acoustic beam out of the metamaterial. A gapless transition between double negative and double positive acoustic metamaterials is realized. The development of this double zero index metamaterial provides new routes to broaden practical applications of acoustic metamaterials.

Metamaterials offer unprecedented opportunity to engineer fundamental band dispersions which enable novel optoelectronic functionalities and devices. Precise control of photonic degrees of freedom can always succeed to manipulate the flow of light. For example, photonic net spin flows such as one-way transports and spin-directional locking have been realized at the boundary of topologically-protected photonic metacrystals. But this is not the only way to achieve net spin flow in solid state systems. Valley degree of freedom may provide a new route to modulate the spin flow in bulk crystals without the assist of boundary. Here, we show the molding of spin flow of light in valley photonic crystals. The coupled valley and spin physics is illustrated analytically. The associated photonic valley Hall effect and unidirectional net spin flow are well demonstrated inside the bulk crystals, instead of the assist of topologically non-triviality. We also show the independent control of valley and topology, resulting in a topologically protected flat edge state. Valley photonic crystals may open up a new route towards the discovery of fundamentally novel states of light and possible revolutionary applications.

Transformation optics provides a powerful tool for controlling electromagnetic fields and designing novel optical devices. In practice, devices designed by this method often require material optical properties that cannot be achieved at visible or near IR light wavelengths. The conformal transformation technique can relax this requirement to isotropic dielectrics with gradient refractive indices. However, there are few effective methods for achieving large arbitrary refractive index gradients at large scales, so the limitation for building transformation optical devices is still in fabrication. Here we present a photoelectrochemical (PEC) silicon etching technique that provides a simple and effective way to fully control the macro scale profiles of refractive indices by structuring porous silicon on the nanoscale. This work is, to our knowledge, the first demonstration of using light to control porosity in p-type silicon. We demonstrate continuous index variation from n = 1.1 to 2, a range sufficient for many transformation optical devices. These patterned porous layers can then be lifted off of the bulk silicon substrate and transferred to other substrates, including patterned or curved substrates, which allows for the fabrication of three dimensional or other more complicated device designs. We use this technique to demonstrate a gradient index parabolic lens with dimensions on the order of millimeters, which derives its properties from the distribution of nanoscale pores in silicon.

Optical cavities are imperative in micro/nanophotonics for their ability to provide resonance feedback and radiation enhancement. In recent years, the interplay between gain and loss using parity-time (PT) symmetry has opened up a new degree of freedom for cavity mode and emission control. I will first discuss a PT micro-ring cavity with the unique features of thresholdless PT symmetry breaking and single-mode lasing. Next, I will reveal a novel PT optical cavity which can support lasing and coherent perfect absorption modes within a single device and enable strong modulation from coherent amplification to coherent absorption.

Layered transition metal dichalcogenide (TMDC) with hexagonal lattice structure has six valleys at corners of the Brillouin zone. The nontrivial Berry curvature distribution renders the adjacent valleys with distinguishable valley angular momentum, which enables itself as an ideal 2D valleytronic platform. Recent studies reported strong excitonic effect in monolayer WS2 and each excitonic state is identified with a well-defined orbital angular momentum, however the anticipated selection rules involve nonlinear optical processes are not clear. Here we show valley angular momentum (VAM) together with exciton angular momentum (EAM) impose different valley-exciton locked selection rules for second harmonic generation (SHG) and two photon luminescence (TPL) in monolayer WS2. Moreover, the two-photon induced valley populations yield net circular polarized photoluminescence after a sub-ps interexciton relaxation. The work demonstrates a new approach to control valley population at different excitonic states for next generation of optical circuits and quantum information computing.

The second harmonic generation (SHG) produced from two-dimensional atomic crystals have been utilized recently in studying the grain boundaries and electronic structure of such ultra-thin materials. However, the SHG in many of these crystals, such as transition metal dichalcogenides (TMDCs), only occur in odd numbered layers with limited intensity due to their noncentrosymmetric nature. Here, we probe the SHG from the bulk noncentrosymmetric molybdenum disulfide (MoS2). Whereas the commonly studied 2H crystal phase’s anti-parallel nonlinear dipoles in adjacent layers give an oscillatory SH response, the parallel nonlinear dipoles of each atomic layer in the 3R phase constructively interfere to amplify the nonlinear light. Due to this interference, we observed the atomically phase-matched condition yielding a quadratic dependence between the intensity and layer number. Additionally, we probed the layer evolution of the A and B excitonic transitions in 3R-MoS2 using SHG spectroscopy and found distinct electronic structure differences arising from the crystal geometry. These findings demonstrate the dramatic effect of the symmetry and layer stacking of these atomic crystals.

We introduce a new family of spectral singularities with highly directional response in parity-time (PT) symmetric cavities. These spectral singularities support modes with infinite reflection from one side and zero reflection from the other side of the cavity, results in simultaneous unidirectional laser and unidirectional reflectionless parity-time symmetric cavity. Such unidirectional spectral singularities emerge from resonance trapping induced by the interplay between parity-time symmetry and Fano resonances.

Quantum vacuum engineering is an active field of research. Here we use recent advances in the field of metasurface (2D-array of sub-wavelength scale nano-antennas) to construct an anisotropic quantum vacuum (AQV) in the vicinity of a quantum emitter located at some macroscopic distance from the metasurface. Such AQV can induce quantum interference among several atomic transitions, even when the transition dipole moment corresponding to the decay channels are orthogonal.
Recently, there have been few theoretical proposal to use metamaterials to engineer the back-action. All these approaches, which works in the near field (few tens of nanometers from the surface), suffers from trapping an atom at these distance, surface interactions like quenching, Casimir force etc. Hence it’s pivotal to construct the back-action over macroscopic distance. We harness the polarization dependent response of a metasurface to engineer the back-action of the spontaneous emission from the atom to itself. We show strong anisotropy in the decay rate of a quantum emitter which is a manifestation of AQV.
Engineering light-matter interaction over macroscopic distances opens new possibilities for long-range interaction between quantum emitters for quantum information processing, spin-optics/spintronics etc.

Perhaps the most successful application of plasmonics to date has been in sensing, where the interaction of a nanoscale localized field with analytes leads to high-sensitivity detection in real time and in a label-free fashion. However, all previous designs have been based on passively excited surface plasmons, in which sensitivity is intrinsically limited by the low quality factors induced by metal losses. It has recently been proposed theoretically that surface plasmon sensors with active excitation (gain-enhanced) can achieve much higher sensitivities due to the amplification of the surface plasmons. Here, we experimentally demonstrate an active plasmon sensor that is free of metal losses and operating deep below the diffraction limit for visible light. Loss compensation leads to an intense and sharp lasing emission that is ultrasensitive to adsorbed molecules. We validated the efficacy of our sensor to detect explosives in air under normal conditions and have achieved a sub-part-per-billion detection limit, the
lowest reported to date for plasmonic sensors with 2,4-dinitrotoluene and ammonium nitrate. The selectivity
between 2,4-dinitrotoluene, ammoniumnitrate and nitrobenzene is on a par with other state-of-the-art explosives detectors. Our results show that monitoring the change of the lasing intensity is a superior method than monitoring the wavelength shift, as is widely used in passive surface plasmon sensors. We therefore envisage that nanoscopic sensors that make use of plasmonic lasing could become an important tool in security screening and biomolecular diagnostics.

Direct oblique plane imaging is a high-speed microscopy technique that observes a sample’s plane that is inclined to the focal plane of the microscope objective lens. This wide-field microscopy is suitable for a study of fast dynamics of living samples where the principle plane of interest is tilted to the focal plane. A way to implement this imaging technique is to use remote focusing together with a tilted mirror, which involves asymmetrical pupil function of the imaging system. We rigorously study the anisotropic resolving power of the oblique plane imaging using a vectorial diffraction theory. From the derived effective pupil function, we calculate vectorial point spread function (PSF) and optical transfer function (OTF). We show that the two-dimensional (2D) PSF of the direct oblique plane imaging is not merely an oblique crosssection of the 3D PSF of circular aperture system. Similarly, 2D OTF of the oblique plane imaging is different from 2D oblique projection of conventional 3D OTF in circular aperture system.

The extremely large speed of light is a tremendous asset but also makes it challenging to control, store or shrink
beyond its wavelength. Particularly, reducing the speed of light down to zero is of fundamental scientific interest
that could usher in a host of important photonic applications, some of which are hitherto fundamentally
inaccessible. These include cavity-free, low-threshold nanolasers, novel solar-cell designs for efficient
harvesting of light, nanoscale quantum information processing (owing to the enhanced density of states), as
well as enhanced biomolecular sensing. We shall here present nanoplasmonic-based schemes where timedependent
sources excite “complex-frequency” modes in uniform (plasmonic) heterostructures, enabling
complete and dispersion-free stopping of light pulses, resilient to realistic levels of dissipative, radiative and
surface-roughness losses. Our theoretical and computational results demonstrate extraordinary large lightdeceleration
factors (of the order of 15,000,000) in integrated nanophotonic media, comparable only to those
attainable with ultracold atomic vapours or with quantum coherence effects, such as coherent population
oscillations, in ruby crystals.

The possibility for controlling both the probe-field optical gain and absorption switching as well as photon
conversion by a surface-plasmon-polariton near field is explored for a quantum dot located above a metal surface.
In contrast to the linear response in the weak-coupling regime, the obtained spectra could show an induced optical
gain and a triply-split spontaneous emission peak resulting from the interference between the surface-plasmon
field and the probe or self-emitted light field in such a strongly-coupled nonlinear system.

Electro-optic modulators have been identified as the key drivers for optical communication. With an ongoing
miniaturization of photonic circuitries, an outstanding aim is to demonstrate an on-chip, ultra-compact, electro-optic
modulator without sacrificing bandwidth and modulation strength. While silicon-based electro-optic modulators have
been demonstrated, they require large device footprints of the order of millimeters as a result of weak non-linear
electro-optical properties. The modulation strength can be increased by deploying a high-Q resonator, however with
the trade-off of significantly sacrificing bandwidth. Furthermore, design challenges and temperature tuning limit the
deployment of such resonance-based modulators. Recently, novel materials like Graphene have been investigated for
electro-optic modulation applications with a 0.1 dB per micrometer modulation strength, while showing an
improvement over pure silicon devices, this design still requires devices lengths of tens of micrometers due to the
inefficient overlap between the Graphene layer and the optical mode of the silicon waveguide. Here we experimentally
demonstrate an ultra-compact, Silicon-based, electro-optic modulator with a record-high 1dB per micrometer
extinction ratio over a wide bandwidth range of 500 nm in ambient conditions. The device is based on a plasmonic
Metal-Oxide-Semiconductor (MOS) waveguide, which efficiently concentrates the optical modes’ electric field into a
nanometer thin region comprised of an absorption coefficient-tuneable Indium-Tin-Oxide (ITO) layer. The modulation
mechanism originates from electrically changing the free carrier concentration of the ITO layer. The seamless
integration of such a strong optical beam modulation into an existing silicon-on-insulator platform bears significant
potential towards broadband, compact and efficient communication links and circuits.

Plasmon lasers are a new class of coherent optical amplifiers that generate and sustain light well below its
diffraction limit [1-4]. Their intense, coherent and confined optical fields can enhance significantly light-matter
interactions and bring fundamentally new capabilities to bio-sensing, data storage, photolithography and optical
communications [5-11]. However, metallic plasmon laser cavities generally exhibit both high metal and radiation
losses, limiting the operation of plasmon lasers to cryogenic temperatures, where sufficient gain can be attained.
Here, we present room temperature semiconductor sub-diffraction limited laser by adopting total internal
reflection of surface plasmons to mitigate the radiation loss, while utilizing hybrid semiconductor-insulator-metal
nano-squares for strong confinement with low metal loss. High cavity quality factors, approaching 100, along with strong λ/20 mode confinement lead to enhancements of spontaneous emission rate by up to 18 times. By controlling the structural geometry we reduce the number of cavity modes to achieve single mode lasing.

Data communications have been growing at a speed even faster than Moore's Law, with a 44-fold increase
expected within the next 10 years. Data Transfer on such scale would have to recruit optical
communication technology and inspire new designs of light sources, modulators, and photodetectors. An
ideal optical modulator will require high modulation speed, small device footprint and large operating
bandwidth. Silicon modulators based on free carrier plasma dispersion effect and compound
semiconductors utilizing direct bandgap transition have seen rapid improvement over the past decade. One
of the key limitations for using silicon as modulator material is its weak refractive index change, which
limits the footprint of silicon Mach-Zehnder interferometer modulators to millimeters. Other approaches
such as silicon microring modulators reduce the operation wavelength range to around 100 pm and are
highly sensitive to typical fabrication tolerances and temperature fluctuations. Growing large, high quality
wafers of compound semiconductors, and integrating them on silicon or other substrates is expensive,
which also restricts their commercialization. In this work, we demonstrate that graphene can be used as the
active media for electroabsorption modulators. By tuning the Fermi energy level of the graphene layer, we
induced changes in the absorption coefficient of graphene at communication wavelength and achieve a
modulation depth above 3 dB. This integrated device also has the potential of working at high speed.

Laser science has tackled physical limitations to achieve higher power, faster and smaller light
sources. The quest for ultra-compact laser that can directly generate coherent optical fields at
the nano-scale, far beyond the diffraction limit of light, remains a key fundamental challenge.
Microscopic lasers based on photonic crystals3, metal clad cavities4 and nanowires can now
reach the diffraction limit, which restricts both the optical mode size and physical device
dimension to be larger than half a wavelength. While surface plasmons are capable of tightly
localizing light, ohmic loss at optical frequencies has inhibited the realization of truly nano-scale
lasers. Recent theory has proposed a way to significantly reduce plasmonic loss while
maintaining ultra-small modes by using a hybrid plasmonic waveguide. Using this approach, we
report an experimental demonstration of nano-scale plasmonic lasers producing optical modes
100 times smaller than the diffraction limit, utilizing a high gain Cadmium Sulphide
semiconductor nanowire atop a Silver surface separated by a 5 nm thick insulating gap. Direct
measurements of emission lifetime reveal a broad-band enhancement of the nanowire's exciton
spontaneous emission rate up to 6 times due to the strong mode confinement and the signature
of apparently threshold-less lasing. Since plasmonic modes have no cut-off, we show downscaling
of the lateral dimensions of both device and optical mode. As these optical coherent
sources approach molecular and electronics length scales, plasmonic lasers offer the possibility to
explore extreme interactions between light and matter, opening new avenues in active photonic
circuits, bio-sensing and quantum information technology.

A new class of optical modes arising from the hybridization between one localized plasmon and two orthogonal
waveguide modes is described. Of particular interest is our observation that these hybrid modes simultaneously exhibit
extremely low-loss and highly dispersive characteristics, which translate into slow light propagation. We propose that
this is a new type of classical analogs of the electromagnetically induced transparency (EIT) in an atomic system. Based
on a fine balance of geometric and material dispersion in the system, destructive interference of the waveguide modes
cancels out the metal loss, resulting in a narrow transparent window within a broad absorption band. In accordance with
the developed phenomenological model, we show that the dispersion characteristics of the hybrid modes can be entirely
controlled by tuning the coupling strengths between the plasmon and waveguide modes while the mode losses remain the
same.

Optical lithography has been the key for continuous size reduction of semiconductor devices and circuits manufacturing. Although the industry is continually improving the resolution, optical lithography becomes more
difficult and less cost effective in satisfying the ever increasing demands in nano-manufacturing. Besides manufacturing,
the dramatic advancements in nanoscale science and engineering also call an urgent need for high-throughput
nano-fabrication technologies that are versatile to frequent design changes. Here we experimentally demonstrated the
capability of patterning with 50 nm linewidth with a high flying speed at 10 meter/second. This low-cost nano-fabrication
scheme has the potential of a few orders of magnitude higher throughput than current maskless techniques, and promises a
new route towards the next generation nano-manufacturing. Besides its application in nanolithography, this technique can also be used for nanoscale metrology, imaging and data storage.

Nanoimprint lithography is used to fabricate a metamaterial with the "fishnet" structure composed of Ag/a-Si/Ag layers
that exhibits negative refractive index in the near-infrared. We have carried out a femtosecond pump-probe experiment
to measure the transient photo-induced response of this structure. With a pump fluence of 330μJ/cm2 at 800nm, the
transmission at the magnetic resonance is increased by ~15.4%. The induced change originated from carrier excitation in
the a-Si layer has a fast decay constant of 1.1ps.

Nearfield scanning optical microscopy (NSOM) offers a practical means of optical imaging at a resolution well beyond
the diffraction limit of the light. However, its applications are limited due to the strong attenuation of the light
transmitted through the sub-wavelength aperture. In this paper, we report the development of particle enhanced
plasmonic nearfield scanning optical microscope (PEP-NSOM) with a high optical coupling efficiency and a high spatial
resolution. Two plasmonic components, a gold nanoparticle and a plasmonic lens, are integrated on a PEP-NSOM probe.
By exciting both propagating surface plasmons and localized surface plasmons, PEP-NSOM probes are capable of
focusing light onto the nanoparticle assembled on the aperture of the plasmonic lens, which can further squeeze the light
to a few tens of nanometers. Nearfield intensity at the focus points of PEP-NSOM probes is 590 times higher than that of
incident light according to numerical simulations. The E-field profile is also shown to be confined laterally <50nm at the
imaging plane, which promises good nearfield images with high spatial resolution and low signal-noise ratio.
Investigation indicates the local intensity enhancement can be further increased to be 4830 when using a gold nanodimer
on the PEP-NSOM probe, which suggests the PEP-NSOM to be an open system of utilizing plasmonic nanostructures
for nano-imaging. By providing a strong nano-scale light source, PEP-NSOM can be used as a high speed nano-scale
imaging tool for single molecule detection and many other applications requiring high temporal/spatial resolution.

The surface plasmons (SPs) eigenproblem which arises in inhomogeneous metal-dielectric films is studied at resonance conditions. We show that short-range correlations present in the governing Kirchhoff Hamiltonian (KH) result in delocalization of the eigenstates at the center of the spectrum. The delocalization is manifested as a power law/logarithmic singularity for the density of states and SPs localization lengths. Based on the SPs eigenproblem, analytical relationships are derived for the electromagnetic response of the semicontinuous film in resonance and off-resonance regimes. Experimental studies indirectly confirm the existence of delocalized SP states in the random system.

By tailoring the dispersion curve of surface plasmons (SPs) of a thin metallic film surrounded by dielectric half-spaces, it is shown that the group velocity of the symmetric mode is always positive, while the group velocity of the anti-symmetric mode can be negative. Consequently, the forward and backward propagation of SPs, in which the energy flow is respectively parallel or antiparallel to the wave vector, can be realized. The physical origin of the intriguing backward SPs is given. Furthermore, schemes for the negative refraction and imaging of SPs are proposed by incorporating two plasmon modes with group velocities of opposite signs.

Surface plasmon polaritons, sometimes referred to as Surface Plasmons (SPs) have brought us great opportunities to
work in nanoscale at optical frequencies. The SPs at the two surfaces of a thin metal film interact with each other, hence
generate new modes which are either symmetric or anti-symmetric. For anti-symmetric modes, the dispersion curve turns
to be of negative slope at large wave vectors, so two different anti-symmetric modes can be excited at the same
frequency. These two modes can form beats with novel features. The envelope (profile) of the beating SP waves could be
stationary, which means its shape will not change in time. Our simulation results clearly showed such phenomena, which
is a strong evidence of the SPs dispersion relations at the thin metal film. It is a proof of the existence of negative group
velocity of SPs. Beats can help us determine the difference in k and the amplitudes ratio of the two beating waves. We
also studied beating between anti-symmetric mode and symmetric mode SPs with the same frequency. The study of the
energy density distribution showed that the output from such system can be well controlled through beats formation.
Example by using NSOM (Near-field Scanning Optical Microscopy) has been simulated. The beating phenomena have a
potential application in the integrated optical circuits.

Recent theoretical and experimental studies have shown that imaging with resolution well beyond the diffraction
limit can be obtained with so-called superlenses. Images formed by such superlenses are, however, in the near
field only, or a fraction of wavelength away from the lens. In this paper, we propose a far-field superlens (FSL)
device which is composed of a planar superlens with periodical corrugation. We show in theory that when an
object is placed in close proximity of such a FSL, a unique image can be formed in far-field. As an example, we
demonstrate numerically that images of 40 nm lines with a 30 nm gap can be obtained from far-field data with
properly designed FSL working at 376nm wavelength.

Nearfield scanning optical microscopy (NSOM) offers a practical means of optical imaging at a resolution well beyond
the diffraction limit of the light. However, its applications are limited due to the strong attenuation of the light
transmitted through the sub-wavelength aperture. To solve this problem we report the development of plasmonic
nearfield scanning optical microscope with a high optical coupling efficiency. By exciting surface plasmons, plasmonic
NSOM probes are capable of focusing light into a 100 nm spot. Both numerical simulation and nearfield exposure
experiments have demonstrated that the intensity at the focal point is at least 10 times stronger than can obtained from
the conventional NSOM probes under the same illumination condition. By providing a strong nano-scale light source,
plasmonic NSOM can be used as a high speed nano-scale imaging tool for cellular visualization, molecule detection, and
many other applications requiring high temporal resolution.

We present S and P polarized measurements of artificial bianisotropic magnetic metamaterials with resonant behavior at infrared frequencies. These metamaterials consist of an array of micron sized (~40μm) copper rings fabricated upon a quartz substrate. Simulation of the reflectance is obtained through a combination of electromagnetic eigenmode simulation and Jones matrix analysis, and we find excellent agreement with the experimental data. It is shown that although the artificial magnetic materials do indeed exhibit a magnetic response, care must be taken to avoid an undesirable electric dipole resonance, due to lack of reflection symmetry in one orientation. The effects of bianisotropy on negative index are detailed and shown to be beneficial for certain configurations of the material parameters.

We employed micro-electro-mechanical system (MEMS) techniques to fabricate parallel sub-wavelength thin-wire structures of metals on elastomeric matrices. From the transmission measurement by Fourier Transform Infrared Spectroscopy, we observed the depressed plasma frequencies of these thin-wire structures at terahertz (THz) ranges. Furthermore, the behavior of depressed plasma frequencies is very sensitive to the polarization of the applied field. The reasons that these engineered materials exhibit unprecedented properties not observed in nature can be interpreted by two factors: the diluted electron densities and the enhancement of electron mass. In addition, the plasma frequencies are readily tunable over a broad frequency range by extending the elastomeric matrices to change their periodicity. These novel properties of tunable and polarization-dependant plasma frequencies at THz ranges promise abundant striking applications in THz optics.

Near-field multiphoton optical lithography is demonstrated by using ~120 fs laser pulses at 790 nm in an apertureless near-field optical microscope, which produce the lithographic features with ~ 70 nm resolution. The technique takes advantage of the field enhancement at the extremity of a metallic probe to induce nanoscale multiphoton absorption and polymerization in a commercial photoresist, SU-8. Even without optimization of the resist or laser pulses, the spatial resolution of this technique is as high as λ/10, nearly a factor of two smaller than the previous multiphoton lithography in the far field.

Nano gold particles interact strongly with visible light to excite the collaborative oscillation of conductive electrons within nano particles resulting in a surface plasmon resonance which makes them useful for various applications including bio-labeling. In this paper, we study the effect of particle sizes with particle plasmon resonant wavelength and the coupling between pair of elliptical metallic disks and ellipsoid particles by simulations and experiments. The red-shift resonant peak wavelength of coupled particles to that of single particle is due to particle plasmons near-field coupling. The shift decays is approximately exponentially with increasing particle spacing, and reaches zero when the gap between the two particles exceeds about 2.5 times the particle short axis length. It is also found that the exponential decay of peak shift with particle gap is size independent but shape dependent.

Strong Raman signals have been observed in various molecules attached to rough metal film surfaces or nano silver/gold particles. This phenomenon is denoted as surface enhanced Raman scattering (SERS). Recent experiments have shown that the effective cross sections of Raman scattering can reach the same level that of fluorescence of good laser dyes, making SERS a promising single-molecular detection tool. The commonly used substrates for SERS consist of colloidal Ag/Au particle aggregates, where SERS active sites, called “hot spots”, are only found by chance and not controllable. The poor repeatability and controllability of these SERS substrates have prevented SERS from viable industrial applications, therefore it is imperative to design and fabricate optimized "hot spots" with desired plasmon resonance frequency in a controllable fashion. In this paper, we present a new class of composite nano particles, which is consisted of stacked alternative metal/dielectric layers, called nanoburger. We study optical properties of these nanoburger particles by using discrete dipole approximation method. The numerical results show that nanoburger particles possess many advantages over single layered particles, including high brightness or scattering intensity, high local field enhancements, and more freedom of tuning plasmon resonance wavelength. Another important merit of the nanoburger particles is that they can be fabricated with traditional micro/nano lithography techniques, and thus are integrable with techniques such as lab-in-a-chip.

Recent theoretical works have suggested the possibility of constructing a diffraction-free lens by using a negative refractive index medium (NRIM). The key theoretical proposition is that evanescent waves can be greatly enhanced by increasing the thickness of the NRIM. We present here experimental evidence on enhanced transmission of evanescent waves via surface plasmon at a thin silver film operating near surface plasma resonant frequency. We found the transmission of evanescent waves rapidly grows with the film thickness up to about 50 nm, after which it decays as loss becomes significant. These experiments also demonstrated the broadening of enhanced transmission spectrum as photon energy approaches plasma resonance εAg = -1 condition. These findings represent the first step toward the understanding and realization of a diffraction-free lens by using NRIM.

Micro-stereolithography (μSL) is capable of fabrication of highly complex three-dimensional (3D) microstructures by selectively photo-induced polymerization from the monomer resin. However, during the evaporative drying of structures from liquid resin, the 3D microstructures often collapse due to the capillary force. In this work, a theoretical model is developed to analyze the deflection and adhesion between thin polymer beams under capillary force. The
detachment length of the test structures and adhesion energy of a typical μSL polymer (HDDA) are obtained experimentally which are important for MEMS structure design. Finally, we successfully developed a sublimation process to release the 3D microstructures without the adhesion.

Heat and mass transfer at the nanosecond time scale and the nanometer length scale in pulsed laser fabrication of ultra-shallow p+-junction is studied in this work. A technique is developed to fabricate the ultra-shallow p+-junctions with pulsed laser doping of crystalline silicon with a solid spin-on-glass (SOG) dopant, through the nanosecond pulsed laser heating, melting, and boron mass diffusion in the 100 nm thin silicon layer close to the surface. High boron concentration of 1020 atoms/cc and the `box-like' junction profile are achieved. The key mechanism determining the `box-like' junction shape is found to be the melt-solid interface limited diffusion. The ultra-shallow p+-junctions with the depth from 30 nm to 400 nm are successfully made by the excimer laser. The optimal laser fluence condition for SOG doping is found about 0.6 - 0.8 J/cm2 by studying the ultra-shallow p+-junction boron profiles measured by the secondary ion mass spectroscopy versus the laser fluence and the pulse number. The 1D numerical analysis agrees reasonably with the experiment, within the available physical picture. Possible mechanisms such as boron diffusivity dependence on the dopant concentration in the molten silicon are proposed.

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